Vegetable crops and ornamental and floral plants can be established in the field or end-use locations in various ways, but principally by direct seeding or transplants grown in containers in greenhouses, protected beds, or open fields. Transplant production is a highly specialized aspect of the greenhouse and nursery industry, one which demands careful attention to plant growth and development-particularly, the choice of the growing medium. Under greenhouse/nursery conditions, field soil, alone, is usually inadequate for reasons relating to aeration and poor drainage. Addition of sand and/or peat improves the use of field soil as a seeding mixture. Artificial mixtures are advantageous in that they address the deficiencies of field soil and are free from pests, bacteria, and the presence of undesirable chemicals.
The most common media used in containerized systems are mixtures of peat and vermiculite or perlite, bark and wood chips, or mixtures thereof. Container types range from wooden troughs to rigid plastic pots to polyethylene bags. Such materials are light-weight for easy handling and movement in and out of a greenhouse setting, can be used for several successive crops, are relatively inexpensive, and easier to manage compared to recirculated hydroponic systems.
As described in the aforementioned co-pending application, white mushroom farming, representative of mushroom production, consists of six steps: Phase I composting and Phase II composting followed by spawning, casing, pinning, and cropping, in succession. Composting involves preparation of the nutrient base (Phase I) and pasteurization/de-ammonifization (Phase II) for the mushrooms. See, Wuest, Duffy, and Royce, Six Steps to Mushroom Farming, Penn State Univ., Col. of Ag. Sci.--Coop. Ext. Spec. Cir. 268 circa 1979, incorporated herein in its entirety. Spawning is the process by which the grower inoculates the compost with the mushroom "spawn", (mushroom mycelia propagated vegetatively).
In Step 4, the spawn-run compost is cased, whereby a top-dressing of selected materials (typically, clay-loam field soil, a mixture of peat moss with ground limestone, or reclaimed, spent compost) is spread uniformly over the surface of the compost on which the mushrooms eventually form. This casing is typically pre-wet to a high moisture level, and thereafter acts as a water reservoir and a place for the growth and fusion of mycelia into rhizomorphs. Without rhizomorphs, no primordia, or pins, form, and there would be no mushrooms. Uniformity of the casing over the compost is very important because it allows the spawn to move into and through the casing at the same rate. Additionally, it is critical that the casing medium be able to hold water, as the continuous availability of moisture is essential for the development of a firm, marketable mushroom of acceptable size, and, ultimately for profitable yields. Throughout the period following casing, water is applied intermittently to maintain the moisture level. Knowing when, how, and how much water to apply to the casing material is considered an art form in the industry and critical to efficient production.
Mushroom initials develop as outgrowths on rhizomorphs formed in the casing. The initials grow in size to form structures referred to as pins, which in turn continue to expand and grow through a button stage and ultimately enlarge into a mushroom. Depending upon growing conditions, mushrooms can be harvested 18-21 days after casing. Pin development can be controlled, in part, by the concentration of carbon dioxide in the atmosphere above the casing. Optimal pin development is dependent upon a time reduction of carbon dioxide concentration, along with maintenance of sufficient moisture and relative humidity. Buttons continue to develop and enlarge through the cropping period. Individual crops or "breaks" are gathered during repeating 3-5 day harvests throughout the cropping phase. Several breaks may be harvested in succession followed by a several day period in which no new mushrooms appear. This break/harvest cycle is repeated several times during cropping, which may last anywhere from 35-150 days depending on the mushroom variety and growing technique.
While each phase or step in the mushroom production process is critical to the growth cycle and the overall yields obtained, the casing Step 4 presents particular problems and the opportunity for unique solutions. Much the same can be said for the production of greenhouse and nursery stock.
One approach, used with limited success is to add the so-called "superabsorbant" polymers to the casing medium to increase moisture availability to the mushroom spawn. None of these additives have met with any degree of commercial success, due to a number of significant problems and deficiencies. First of all, the superabsorbants are highly cross-linked polymers which form gel networks, absorbing many times their weight in water. However, due to their high gel strength the superabsorbants (hydrogels) do not readily give up their water to the growing mushroom mycelia. Second, because these superabsorbant polymers are gels and water-insoluble under use conditions, they present a discontinuous lump, or water reservoir, which is only available to mycelium in the immediate vicinity of the gel network. As a result, they do not coat the peat strands. Third, at the concentrations used in mushroom production (1-3% by weight), they do not form a supply of water sufficient for the growing mushrooms and, in fact, compete with the growing mushroom mycelium for the available water supply. Fourth, they are difficult to add to the casing mixture because of their tendency to agglomerate and clump. The superabsorbants do not wet out on a peat strand and are difficult to uniformly mix throughout the casing. Fifth, additives of this sort are expensive, averaging about $6.00 per pound, and available only at costs which unduly cut profit margins and render them unfeasible for widespread use. Finally, the superabsorbants of the prior art are adversely affected by osmotic pressures induced by the presence of ionic concentrations. This phenomenon is observed dramatically with the collapse of the gel/matrix in the presence of commercial fertilizer and subsequent loss of water retention.
Ornamental and floral nursery stock and many vegetables including but not limited to tomatoes, peppers, broccoli, cauliflower, lettuces, and celery are cultivated commercially in greenhouses from seeds for transplant to the field and later use by growers ranging from the backyard gardener to the corporate commodity producer. The grower has an interest in purchasing hardy, vigorous stock which will withstand the trauma of handling, shipment, and transplanting with minimal growth interruption. In addition to providing such a product, the nursery has an interest in maximizing greenhouse production over the course of a growing season. However, many efforts to decrease growth cycle time and increase greenhouse productivity have resulted in stock incompatible with nursery handling techniques and ill suited to meet grower requirements.
In summary, a considerable number of drawbacks and problems exist in the art relating to synthetic polymers for use as additives to casings in mushroom production and to growth media for vegetable seedlings, ornamental nursery stock, and sod/turf. Standard cultivation practices define a need for a casing material and/or an amendment which facilitates the ability of the mushroom mycelia to move therethrough and maximizes access to the available water and nutrient supply. Likewise, a support material/growth medium and/or amendment which increases the media retention of water and uptake of nutrients by vegetables, ornamental and floral plants, and sod/turf has been an ongoing concern in the art.